Smart windows: a critical view

Residential windows are a major source of energy loss, unwanted heat gains, air leakage and glare. Windows are a weak thermal point in the home’s shell.

Why not then consider super-insulated, thermally efficient windows with smart glazing?

According to a leading window manufacturer (Alpen), smart windows - with "smart glazing" - can «block summer heat, retaining winter warmth, eliminating harmful ultraviolet rays, and maximizing natural daylight and clarity and … architectural freedom».

Alpen is a leading manufacturer, but there are other companies claiming similar results, like Ravenbrick, Pleotint, View or Sage.

These last companies are using a special technology - the so-called electrochromic technology - to make the glazing of the windows responsive to the outdoor temperature. When the temperature rises above a certain point, a filter is automatically activated, transitioning the window to a tinted state, which blocks unwanted ultraviolet radiation and heat gains (reducing air conditioning needs).

There are three main types of smart glass – electrochromic and thermochromic and photochromic. All work based on the same principle: they are able to control the amount of incoming heat, according to the temperature of the outer pane glazing; they can automatically admit five times more heat gains on cold winter days than on summer ones – a great feature to reduce cooling bills, but also to reduce heating consumption (by minimizing heat loss during the winter).

Around for some years

Smart glazing-windows aren't exactly new. They have been around for some years now.

But like other very promising technologies with the potential to revolutionize our future, they are not mature yet, and their current scope and advantages are limited. And we should not forget it. Smart windows have to prove themselves yet.

Electrochromic windows cost twice as much as current energy-efficient windows. And their durability and long-term performance is not yet well tested.

Most of all we don’t have to wait for this and other technologies to achieve Zero Energy Houses, or other very energy efficient buildings consuming very little energy. We have already the know-how and the technologies to carry it out.

Bottom line

Sticking to high-energy efficient windows – with top glazing and fiberglass or vinyl foam-filled frames, like those offered by a few Canadian and German manufacturers  - is still the best option. Issues such as the right size of the windows for the different sides of the house will continue to be of the highest importance, above the claims of window manufacturers.



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